Line protector for a communication circuit

ABSTRACT

A plug-in line protector for a communications circuit provides protection for overvoltage and overcurrent conditions of the line. A module containing carbon blocks provides an air gap in an overvoltage shunt circuit for grounding high voltage transients. For an overcurrent condition in that shunt circuit, a solder pellet melts causing contacts in an overcurrent shunt circuit to engage and ground the line. The protector also has an overcurrent responsive mechanism in the form of a heat coil in the line. When the coil is heated, it melts the solder pellet and closes the contacts in the overcurrent shunt circuit. One of those contacts is a bobbin around which the heat coil is wrapped and which serves to transfer heat to the solder pellet.

United States Patent [1 1 Baumbach LINE PROTECTOR FOR A COMMUNICATIONCIRCUIT [75] Inventor: Bertram W. Bnumbach, Arlington Heights, Ill.

[73] Assignee: Reliable Electric Company, Franklin Park, Ill.

[22] Filed: Aug. 24, 1972 [21] Appl. No.: 283,492

[52] US. Cl 317/16, 317/615, 337/15, 337/32 [51] Int. Cl. H02h 3/38 [58]Field of Search 337/32, 33, 15; 317/16, 31, 61.5

[56] References Cited UNITED STATES PATENTS 3,255,330 6/1966 MacKenzieet al. 337/34, X 3,573,695 4/1971 Geyer et al. 337/32 X [111 3,743,888[451 July 3,1973

Att0rney- Roy H. Olson. Richard R. Trexler ct al.

[5 7] ABSTRACT A plug-in line protector for a communications circuitprovides protection for overvoltage and overcurrent conditions of theline. A module containing carbon blocks provides an air gap in anovervoltage shunt circuit for grounding high voltage transients. For anovercurrent condition in that shunt circuit, a solder pellet meltscausing contacts in an overcurrent shunt circuit to engage and groundthe line. The protector also has an overcurrent responsive mechanism inthe form of a heat coil in the line. When the coil is heated, it meltsthe solder pellet and closes the contacts in the overcurrent shuntcircuit. One of those contacts is a bobbin around which the heat coil iswrapped and which serves to transfer heat to the solder pellet.

LINE PROTECTOR FOR A COMMUNICATION CIRCUIT CROSS-REFERENCE TO RELATEDAPPLICATION Reference may be had to my copending application Ser. No.187,018 filed Oct. 6, 1971.

BACKGROUND OF THE INVENTION SUMMARY AND OBJECTS OF THE INVENTION Theprotector is typically designed for protection of two lines of acommuncations circuit. Each circuit is provided with protection againstboth overvoltage and overcurrent. For this purpose an arrester module isprovided for each circuit. When an overvoltage of short duration isapplied to either or both of the incoming lines connected to theprotector, the protector provides an arc gap path in an overvoltageshunt circuit to ground so that the overvoltage does not reach insideequipment or central office equipment. When an overvoltage fault is ofprolonged duration, or an overcurrent voltage is such that there isarcing across the arc gap, the current passing through the overvoltageshunt circuit generates sufficient heat to melt a fusible solder pelletin the overvoltage shunt circuit. Then the line will be grounded throughan overcurrent shunt circuit. Inaddition, there is a heat coil in theline circuit for supplying heat to melt the solder pellet in the eventof an overcurrent condition that may not cause arcing across the arcgap. In such case the solder pellet will melt and close the overcurrentshunt circuit to ground. The module contains normally spaced apartcontacts in the form of a cup and a bobbin, both surrounded by aninsulating sleeve to prevent possible arc-over between the adjacentmodule for the other line. These contacts are in the overcurrent shuntcircuit. The cup rests on the metallic ground strip. The heat coil iswrapped around a shaft on the bobbin whereby heat from the heat coilheats the bobbin which in turn transmitsheat to the solder pellet. Theupper end of the bobbin shaft has an insulator with a peripheral metalring, and the heat coil is connected to the peripheral ring and bobbin.The ring and bobbin along with the heat coil are in series with theline. The bobbin and ring are respectively engaged by contact membersthat connect to line terminal pins of the protector. One of thecontactmembers constitutes a springthat urges together the contacts ofthe overcurrent shunt circuit upon melting of the solder pellet eitherby the heat coil or by current through the overvoltage shunt circuit.

Accordingly, it is an object of this invention to provide a lineprotector of the type stated in which overvoltage and overcurrentprotection are provided, and wherein a heat coil in the line circuit isuniquely positioned in proximity to a solder pellet in the overvoltageshunt circuit such that the solder pellet can be melted by sufficientcurrent in the overvoltage shunt circuit or sufficient heat that isgenerated by the heat coil.

Another object of this invention is to provide a line protectorembodying a heat coil and bobbin assembly that is simple and can be massproduced at relatively low cost.

Another object of this invention is to provide a protector of the typestated in which the heat coil is reuseable in that only the solderpellet need be replaced to restore the unit to normal operation.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a perspective view of aplug-in type of line protector constructed in accordance with andembodying the present invention;

FIG. 2 is a fragmentary side view in section of the protector;

FIG. 3 is a fragmentary front view in partial section of the protector;

FIG. 4 is an enlarged fragmentary portion of FIG. 3 in the region of theheat coil; and

FIG. 5 is a view similar to FIG. 4 and showing one of the arrester unitsafter melting of the solder pellet therein.

DETAILED DESCRIPTION Referring now in more detail to the drawing,designates a protector for a pair of communcations lines. However, itwill be appreciated that the principles of the invention are applicableto a protector for a single line only.

The protector 10 comprises a base and an elongated detachable housing 16of generally rectangular cross section. The base 15 and housing 16 areof a suitable dielectric plastic material. The housing 16 may be securedto the base 15 by bosses 17 which snap into correspondingly shapedopenings in the side walls of the housing 16. The upper end of thehousing 16, namely that remote from the base 15, may have a neck portion18 terminating in a flange 19 by which the protector may be gripped forremoval from and placement into a receptacle.

Mounted in and projecting outwardly from the base 15 is a series ofconductive plug-in terminal pins identified by the reference numerals-30 inclusive. In the form of the invention shown, there is a first linepin 25, a first central office pin 29, a second line pin 26, a secondcentral office pin 30, a polarizing pin 28, and a ground pin 27. Thefirst line pin 25 and the first central office pin 29 are components inone of the lines through the protector 10 while the second line pin 26and second central office pin are components in the other line throughthe protector 10. The ground pin 27 is common to both lines while thepolarizing pin 28 is an unconnected or dummy pin that assures properorientation of the protector unit when it is plugged into itsreceptacle.

The pin 25 is electrically and mechanically connected to a contactmember which is formed of flat spring-like material. As best shown inFIG. 2, the contact member 35 has a base portion 37 that seats on anelongated rib 38 on the base 15. The base portion 37 has a flange 50 atwhich the pin 25 is staked. In like manner, contact member 42, which isidentical to contact member 35, is connected to the pin 26.

An additional contact member is staked at its bottom flange 39 to thepin 29. Likewise, a contact 41 of a construction similar to that of thecontact 40 is staked to the pin 30.

For each of the two lines there is provided a removable and replaceablearrester module 60 for providing a first shunt circuit to the ground pin27 in the event of an overcurrent condition and a second shunt circuitto the ground pin in the event of an overvoltage condition. The modulesare identical and each includes metallic contacts in the form of abobbin 62 and cup 64. The bobbin 62 and cup 64 are surrounded by aninsulating sleeve 66. Within the cup 64 is a carbon arc gap assemblycomprising carbon blocks 68, 70 and an insulating member 72. The carbonblock 68 is suitably bonded to the insulating member 72, the latterbearing at one end against the carbon block 70 to constitute a spacer sothat an air gap 74 is established between the carbon blocks 68, 70. Theair gap 74 is determined by the minimum arc-over voltage for which theunit is designed. A fusible solder pellet 76 is interposed between thecarbon block 68 and the bobbin 62 so that in the normal operatingcondition of the unit, the cylindrical base or disc part 63 of thebobbin and the edge of the cup 64 are maintained spaced apart.

The upwardly extended parts of the respective contact members 35, 42,40, 41 lie in grooves 78 formed in sidewalls of the housing 16. Each ofthose upwardly extending parts of the contact members 35, 42 terminatesin a downwardly extending generally V shaped portion 80 which bearsfirmly against upper end of the shaft 65 of the associated bobbin 62.Thus, each contact member 35, 42 constitutes a spring tending to urgethe bobbin 62 toward the cup 64; however, engagement of the cup 64 andslug 62 is prevented, in the normal operation of the protector, by thesolder pellet 76.

The bobbin shaft 65 is diametrally reduced to form a shoulder 71 forsupporting a cylindrical insulating member 73. An enveloping metalliccontact ring 75 is secured to the periphery of the insulating member 73for sliding engagement with the downwardly turned end 77 of the contact40 or 41, as the case may be. A heat coil of wire 79 is wrapped aroundthe bobbin shaft 65 intermediate the shoulder 71 and disc 63 and withthe ends of the heat coil 79 being soldered to the peripheral part ofthe disc 63 and to the ring 75. The bobbin shaft 65 is hollow which istapered for mounting on a mandrel so that the heat coil may be wound inplace.

In the normal operating condition of the protector, current flows in aline circuit running from pin 29, through contact member 40, ring 75,heat coil 79, bobbin 62, contact member 35 and to pin 25. In the otherline circuit from pin 26 to pin 30 the current flow is through contactmembers 41, 42, and the heat coil, bobbin and contact ring of theassociated module 60.

A grounding strip 45 has a depending leg 48 that is staked to the groundpin 27. The bottoms of the respective cups 64 rest upon the groundingstrip 45 whereby the cups 64 are grounded. On opposite sides of the leg48 the grounding strip 45 has thin dielectric tape strips 52, 52 whichare downwardly presented and are against the base portions of thecontacts 35, 42. The tape strips 52, 52 insulate the cups 52 from thecontact members 35, 42.

When an overvoltage condition of relatively short duration is applied toone of the lines, for example at pin 25, the contact 35 provides aconductive path through its upper V shaped end 80, through bobbin 62,solder pellet 76 and to carbon block 68. If the overvoltage is at pin29, the contact member 40 provides the conductive path throughthe heatcoil 79 to the bobbin 62.

This overvoltage transient will arc across gap 74 to carbon block andwill be grounded through the grounding strip 45 to the ground pin 27.Under such conditions the solder pellet 76 does not melt. The componentsof the protector remain in the condition shown for instance in FIG. 2,and nothing need be done to restore the protector to its normaloperating condition. Similarly, if an overvoltage condition appears onthe other line, namely the line in which pins 26 and 30 are located, theground is through the contact 41 or 42 and the module 60 associatedtherewith, in the manner previously described.

An overcurrent condition may appear in one of the lines due to aprolonged voltage that is above arcing voltage. Assuming that suchovercurrent conditions appears on the line containing pin 25 and pin 29the current through the associated module 60 will cause the solderpellet 76 to melt, as shown in FIG. 5, since the solder pellet is in theovervoltage shunt circuit. When the solder pellet 76 melts, the springforce applied by the contact 35 moves the bobbin 62, heat coil 79 andinsulator 73 as a unit while maintaining the contact member 35 againstthe bobbin end and maintaining the contact member 40 against the ring75. This spring force causes the bobbin disc 63 to engage the upper edgeof the cup 64 whereby a metallic ground connection to the ground pin 27is made through grounding strip 45. The base of the cup 62 is pressedfirmly against the grounding strip 45 by reason of the spring pressurefrom the contact 35 so as to insure a low resistance flow path for thecurrent. If an overcurrent condition as aforesaid, appears in the linecontaining the pins 26, 30, a ground connection through to the pin 27will result in the manner just described, except that the ground will bethrough contact member 41 or 42 and the corresponding parts in theassociated arrester module 60.

If desired, the plastic strips 52 may be of a type that will melt ifsufficient heat is transmitted thereto from the carbon block 70 throughthe cup 64. This may occur in some kinds of overcurrent conditions, forinstance where there is sufficient voltage for arc-over but the currentis insufficient to melt the solder pellet. Melting of the plastic strip52 results in a short metallic path to ground from the contact member 35or 42, as the case may be, and the spring pressure of the contact member35 or 42 will push the resilient strip 45 against the base portion 37 ofthe contact member.

Overcurrent protection is also afforded by the heat coil 79 that is ineach module 60 and hence in each line circuit. The operation of the heatcoil for each line circuit is the same and so it will suffice todescribe such operation for one line circuit, for instance the circuitwith pins 25 and 29. y

The heat coil 79 is designed to produce sufficient heat to melt thesolder pellet 76 when a predetermined amount of current in magnitudeand/orduration flows through the line circuit. This current may appearin the line circuit even though the voltage produced at the arc gap isinsufficient for arc-over, and such current may, without protectiontherefrom, damage equipment in the line. Accordingly, when suchovercurrent condition heats the wire of the heat coil 79, the heat istransmitted to the bobbin 62. The bottom of the disc 63 seats againstthe solder pellet 76 over a relatively large area so that heat from thebobbin is readily transmitted to the solder pellet 76 causing it tomelt, as shown in FIG.

5. Thereafter, the spring pressure from contact member 35 pushes thebobbin disc 63 against the upper edge of the cup 64 to complete theovercurrent shunt circuit to the grounding strip 45 and to the groundpin 27.

The protector can be restored to normal operation by removing thehousing 16 and then removing the affected module 60. The module 60 maybe disassembled, the melted solder of the solder pellet may be removed,a new solder pellet may then be installed, and then the parts can bereassembled. The heat coil 79, bobbin 62 and insulating member 73 may bereused, thereby reducing the cost of restoring the protector.

The invention is claimed as follows:

1. A line protector for a communications circuit, said protector havingline terminals and a line circuit connected therebetween, a groundterminal, a first normally open shunt circuit from said line circuit tosaid ground terminal, said first shunt circuit having contacts, springmeans biasing said contacts toward each other, a solder element normallymaintaining said contacts apart in opposition to said spring means, anda second shunt circuit from said line circuit to ground, said secondshunt circuit including blocks forming an arc gap, said solder elementbeing in series with said blocks, whereby an overvoltage of shortduration in said second shunt circuit produces an are at said gapwithout melting of said solder element and an overvoltage condition oflonger duration also produces said arc and causes said solder element tomelt and close said contacts, said line circuit including meansresponsive to an overcurrent condition therein and in close proximity tosaid solder element for melting said solder element, whereby anovercurrent condition in either said line circuit or said second shuntcircuit closes said first shunt circuit.

2. A line protector according to claim 1 in which said last-mentionedmeans comprises a coil of wire in series with the line terminals forgenerating heat in response to said overcurrent condition in said linecircuit, and a metallic member around which said coil is wrapped fortransmitting heat to said solder element.

3. A line protector according to claim 2 in which said metallic membercomprises a bobbin having a disc that engages said solder element and ashaft around which the coil is wrapped.

4. A line protector according to claim 3 in which said shaft has aninsulating member mounted thereon, said insulating member having aperipheral metal ring, and said coil is connected to said ring and tosaid bobbin so that said bobbin, said coil and said ring form a seriescircuit.

5. A line protector according to claim 4 including contact members inelectrical connection with said line terminals respectively and withsaid ring and said bobbin respectively.

6. A line protector according to claim 1 in which said last-mentionedmeans comprises a heat coil in series with said line terminals.

7. A line protector according to claim 2 in which said metallic memberalso comprises one of said contacts in said first shunt circuit.

8. In a line protector for a communications circuit that includescontacts, a solder element normally main taining said contacts spacedapart, and spring means urging said contacts together in opposition tosaid solder element; one of said contacts comprising a metallic memberfor transmitting heat to said solder element, a coil of wire wrappedaround said metallic member, an insulating member on said metallicmember, and a metallic ring peripherally secured to said insulatingmember.

9. In a line protector according to claim 8, said metallic member havinga shaft upon which said insulating member is mounted, and said coil iswrapped around said stem.

10. In a line protector according to claim 8, said insulating member,said metallic member, and said coil being movable as a unit by saidspring means upon melting of said solder element.

1. A line protector for a communications circuit, said protector havingline terminals and a line circuit connected therebetween, a groundterminal, a first normally open shunt circuit from said line circuit tosaid ground terminal, said first shunt circuit having contacts, springmeans biasing said contacts toward each other, a solder element normallymaintaining said contacts apart in opposition to said spring means, anda second shunt circuit from said line circuit to ground, said secondshunt circuit including blocks forming an arc gap, saiD solder elementbeing in series with said blocks, whereby an overvoltage of shortduration in said second shunt circuit produces an arc at said gapwithout melting of said solder element and an overvoltage condition oflonger duration also produces said arc and causes said solder element tomelt and close said contacts, said line circuit including meansresponsive to an overcurrent condition therein and in close proximity tosaid solder element for melting said solder element, whereby anovercurrent condition in either said line circuit or said second shuntcircuit closes said first shunt circuit.
 2. A line protector accordingto claim 1 in which said last-mentioned means comprises a coil of wirein series with the line terminals for generating heat in response tosaid overcurrent condition in said line circuit, and a metallic memberaround which said coil is wrapped for transmitting heat to said solderelement.
 3. A line protector according to claim 2 in which said metallicmember comprises a bobbin having a disc that engages said solder elementand a shaft around which the coil is wrapped.
 4. A line protectoraccording to claim 3 in which said shaft has an insulating membermounted thereon, said insulating member having a peripheral metal ring,and said coil is connected to said ring and to said bobbin so that saidbobbin, said coil and said ring form a series circuit.
 5. A lineprotector according to claim 4 including contact members in electricalconnection with said line terminals respectively and with said ring andsaid bobbin respectively.
 6. A line protector according to claim 1 inwhich said last-mentioned means comprises a heat coil in series withsaid line terminals.
 7. A line protector according to claim 2 in whichsaid metallic member also comprises one of said contacts in said firstshunt circuit.
 8. In a line protector for a communications circuit thatincludes contacts, a solder element normally maintaining said contactsspaced apart, and spring means urging said contacts together inopposition to said solder element; one of said contacts comprising ametallic member for transmitting heat to said solder element, a coil ofwire wrapped around said metallic member, an insulating member on saidmetallic member, and a metallic ring peripherally secured to saidinsulating member.
 9. In a line protector according to claim 8, saidmetallic member having a shaft upon which said insulating member ismounted, and said coil is wrapped around said stem.
 10. In a lineprotector according to claim 8, said insulating member, said metallicmember, and said coil being movable as a unit by said spring means uponmelting of said solder element.